More particularly, the invention relates to an actuating device for causing a turbine shaft train to rotate. The shaft train comprises the rotors of each turbine module, as well as that of the alternator. The rotation of the shaft train, also referred to as turning, is generally achieved with the help of an electric motor capable of overcoming the resistive torque of the shaft train. The electric motor drives a reduction gear which actuates the shaft train. It is necessary to maintain the rotation of the shaft train during periods of starting and stopping the turbine-generator set in order to equalize the temperatures of the rotor and thereby to avoid any bending of the shaft train under the effect of thermal dissymmetry. The electric motor also allows the rotation of the shaft train to be initiated during a starting phase ahead of the injection of steam into the turbine. The speed of rotation of the shaft train is low and constant during these phases. It varies from a few revolutions per minute to a few tens of revolutions per minute depending on the turbine-generator sets concerned.
However, a turning gear controlled by an electric motor does not allow a very low speed of rotation to be achieved, or the low-amplitude angular displacements of the shaft train that are necessary during maintenance operations.
The object of the present invention is thus to overcome these disadvantages by proposing an actuating device for a turbine shaft train as well as a turbine-generator set.